The invention presented concerns a device for generating mechanical vibration, intended primarily for dynamic compaction of various sorts of material.
For compacting various materials, e.g., in the construction of roads, airfields, vibratory compaction equipment is used to increase the compaction capacity and optimise the result of the compaction work. Optimisation can consist, for example, of increasing the density of the material, increasing its bearing capacity, achieving a certain density profile with regard to depth and of obtaining a particular surface structure. The equipment used can, for example, be rollers that have one or more vibrating drums, self-propelled vibratory plates, vibratory pokers and tampers.
To create the vibration, various types of mechanical systems having rotating eccentrics that utilise centrifugal force are used. This gives in space a rotating circular force vector and in time a sine shaped force vector in a certain direction.
To optimise compaction with regard to properties of the compacted material it is necessary that the vibration be given varying frequency, amplitude and direction.
Known vibratory devices with rotating eccentrics alter parameters of the force vector in the following way:
Examples of systems with one eccentric for achieving a circular force vector with variable amplitude:
See
U.S. Pat. No. 5,618,133 Vibrating mechanism and apparatus for generating . . .
U.S. Pat. No. 4,342,523 High-low force amplitude device
U.S. Pat. No. 4,221,499 Vibratory device
U.S. Pat. No. 3,966,344 Adjustable vibratory roller
Amplitude of the vibration is changed in that the centre of mass for the eccentric weight is displaced in relation to the rotation centre of the eccentric. The vibration frequency is set with the speed of rotation of the rotating eccentric. This is achieved at present by some type of mechanical system.
Systems with two eccentrics:
See U.S. Pat. No. 5,797,699 Process and apparatus for dynamic soil compaction. A linear force vector is obtained by the two eccentrics rotating in different directions of rotation and fully synchronised, ie, at the same speed of rotation. By phase displacement of the eccentrics so that the direction is changed as the eccentrics pass each other, the force vector can be controlled to act in varying directions. Phase displacement of the eccentrics is made by a mechanical system. Vibration frequency is set with the speed of rotation of the rotating eccentrics.
Characteristic for present vibration systems is that they only permit some specific form of vibration and that complicated mechanical devices are required.
The object of the invention presented is to optimise compaction with consideration to many different types of material being compacted using one and the same device.
The arrangement of the invention is for generating a mechanical vibration including: a mass; first and second force cells for generating first and second rotating force vectors to form a resultant force acting on the mass to impart mechanical vibration thereto; the first force cell including a first rotating eccentric to generate the first rotating force vector; an electrically controlled first drive for rotating the first rotating eccentric; and, a first angle sensor for detecting the angular position of the first rotating eccentric relative to a reference direction and outputting a first signal indicative thereof; the second force cell including a second rotating eccentric to generate the second rotating force vector; an electrically controlled second drive for rotating the second rotating eccentric; and, a second angle sensor for detecting the angular position of the second rotating eccentric relative to the reference direction and outputting a first signal indicative thereof; and, the electrically controlled first drive being separate from the electrically controlled second drive.